The chemical oxygen demand (COD) measurement method, whether it is the reflux method, the rapid method or the photometric method, uses potassium dichromate as the oxidant, silver sulfate as the catalyst, and mercury sulfate as the masking agent for chloride ions. Under the acidic conditions of sulfuric acid Determination of COD Determination method based on digestion system. On this basis, people have carried out a lot of research work for the purpose of saving reagents, reducing energy consumption, making the operation simple, fast, accurate and reliable. The rapid digestion spectrophotometric method combines the advantages of the above methods. It refers to using a sealed tube as the digestion tube, taking a small amount of water sample and reagents in the sealed tube, placing it in a small constant temperature digester, heating it at constant temperature for digestion, and using spectrophotometer The COD value is determined by photometry; the specification of the sealed tube is φ16mm, the length is 100mm~150mm, the opening with a wall thickness of 1.0mm~1.2mm is a spiral mouth, and a spiral sealing cover is added. The sealed tube has acid resistance, high temperature resistance, pressure resistance and anti-explosion properties. A sealed tube can be used for digestion, called a digestion tube. Another type of sealed tube can be used for digestion and can also be used as a colorimetric tube for colorimetry, which is called a digestion colorimetric tube. The small heating digester uses an aluminum block as the heating body, and the heating holes are evenly distributed. The hole diameter is φ16.1mm, the hole depth is 50mm ~ 100mm, and the set heating temperature is the digestion reaction temperature. At the same time, due to the appropriate size of the sealed tube, the digestion reaction liquid occupies an appropriate proportion of the space in the sealed tube. A part of the digestion tube containing reagents is inserted into the heating hole of the heater, and the bottom of the sealed tube is heated at a constant temperature of 165°C; the upper part of the sealed tube is higher than the heating hole and exposed to the space, and the top of the tube mouth is lowered to about 85°C under natural cooling of the air; The difference in temperature ensures that the reaction liquid in the small sealed tube is in a slightly boiling reflux state at this constant temperature. The compact COD reactor can accommodate 15-30 sealed tubes. After using a sealed tube for digestion reaction, the final measurement can be done on a photometer using a cuvette or colorimetric tube. Samples with COD values of 100 mg/L to 1000 mg/L can be measured at a wavelength of 600 nm, and samples with a COD value of 15 mg/L to 250 mg/L can be measured at a wavelength of 440 nm. This method has the characteristics of small space occupation, low energy consumption, small reagent consumption, minimized waste liquid, low energy consumption, simple operation, safe and stable, accurate and reliable, and suitable for large-scale determination, etc., making up for the shortcomings of the classic standard method.
Lianhua COD precast reagent vials operation steps:
1. Take several COD precast reagent vials (range 0-150mg/L, or 20-1500mg/L, or 200-15000mg/L) and place them on the test tube rack.
2. Accurately take 2ml of distilled water and put it into the No. 0 reagent tube. Take 2ml of the sample to be tested into another reagent tube.
3. Tighten the cap, shake or use a mixer to mix the solution thoroughly.
4. Put the test tube into the digester and digest at 165° for 20 minutes.
5. When the time is up, take out the test tube and leave it for 2 minutes.
6. Put the test tube into cold water. 2 minutes, cool to room temperature.
7. Wipe the outer wall of the test tube, put the No. 0 tube into the COD photometer, press the “Blank” button, and the screen will display 0.000mg/L.
8. Place other test tubes in sequence and press the “TEST” button. The COD value will be displayed on the screen. You can press the print button to print out the results.
Post time: May-11-2024
